One evolutionary trend in telephony is currently proceeding in the direction of integrated services digital networks (ISDNs) which feature the support of a wide range of voice and data applications in the same network. The ISDN concept emphasizes versatility which may be seen in the wide variety of applications that can be supported. This evolution towards an ISDN system features digital end-to-end connectivity by extending digital technology to the user ends.
Standards for ISDN are based on a layered protocol structure which first appeared as a series of ISDN Recommendations published by The International Telegraph and Telephone Consultative Committee (CCITT) under the title Integrated Services Digital Network (ISDN) Volume III, Fascicle III.5, 1984. These published recommendations initiated considerable development of ISDN systems generally, together with various service trials on an international scale. It is apparent that the utility and consequent success of ISDN depends greatly on the ability of both systems and products developed according to these recommendations to interwork with each other. The integration of devices and networks in conformance with ISDN standards laid down in the recommendations may only be achieved, however, through well defined testing procedures.
In order t o ensure compliance with ISDN specifications and proper operation of network interfaces, all products are required to undergo rigorous testing prior to placement into the field. Since ISDN products are complex devices, extremely specialized test procedures and equipment are required to ensure accuracy in all test procedures.
In the present early phase of ISDN deployment, there is usually no network to transport ISDN traffic between the site of a test system and the development site of a system under test which are often geographically displaced. Consequently ISDN testing is generally conducted either in the test lab or "in-factory", with both the test system and the system under test located at the same site.
A common difficulty associated with "in-lab" testing relates to the problem of operating the system under test in an environment that is dissimilar to that of its development. Although development personnel need to come to the test lab to operate the equipment, they may not have all the development tools needed to support the new equipment when unexpected problems are uncovered during testing. Furthermore, the newly developed equipment may be cumbersome and difficult to move to a testing centre. A typical example would be a large PBX. "In-factory" testing requires that the test lab send a portable tester, together with expert personnel well versed in protocol, to the development site to conduct tests. Therefore, instead of transporting equipment to a test lab, a scaled-down version of the test lab is transported to the equipment.
In either "in-lab" or "in-factory" testing, there is the problem of mobilizing and coordinating expert personnel who will likely have to operate in an unfamiliar environment, without the support to which they are accustomed. This impacts negatively on the productivity of such personnel.
To effectively address the aforedescribed problems, remote testing is needed. Prior to this invention, however, the only known method for remote testing of ISDN protocols was to conduct such testing over telephone lines.
Remote testing of ISDN protocols over telephone lines provides only a partial solution at best since three problem areas are readily identified. The first is the necessity to modify the standard physical interface of the ISDN basic rate access equipment, both at the system under test and the test system interfaces, to allow connection to the transmission equipment interface of the telephone network which operates at a much lower rate. The second problem area concerns the poor transmission quality over long haul telephone lines. The transmission errors introduced may seriously affect the testing by falsifying the test results. The third problem area is the difficulty in setting up the circuits and transmission equipment needed for ISDN protocol testing.
In addition to the above problems, the communication costs of remote testing over telephone lines are very high compared to costs incurred when using the present invention.